This will be used to perform a best-effort rendering, where an error in
rendering won't abort the whole rendering operation, but instead will be
stored for later reference while rendering continues.
We have a new, improved string type coming up in AK (OOM aware, no null
state), and while it's going to use UTF-8, the name UTF8String is a
mouthful - so let's free up the String name by renaming the existing
class.
Making the old one have an annoying name will hopefully also help with
quick adoption :^)
